Polybutylene terephthalate (PBT) is a well-known semi-crystalline resin that has desirable properties. Compared to amorphous resins such as ABS, polycarbonate, and polystyrene, a crystalline resin like PBT will show much better solvent resistance, higher strength, and higher stiffness due to the presence of crystalline spherulites in the resin. PBT resin is used in many applications where its solvent resistance, strength, lubricity, and rigidity are needed, commonly in durable goods that are formed by injection molding, such as in electronic and communications equipment, computers, televisions, kitchen and household appliances, industrial equipment, lighting systems, gardening and agricultural equipment, pumps, medical devices, food handling systems, handles, power and hand tools, bobbins and spindles, and automotive parts in both under-the-hood and exterior applications. PBT is very widely used to form electrical connectors. Through its many blended products, PBT can be tailored to meet a wide variety of end uses.
U.S. Pat. Nos. 7,129,301; 6,020,393; 4,328,059, and United States Publication No. 2005/0113534 disclose various catalysts for the polymerization of polyesters. Tetraalkyl titanates have been most commonly used as catalysts for PBT polymerization. The various titanates can include tetraisopropyl titanate, tetrabutyl titanate, and tetra(2-ethylhexyl) titanate. JP 60147430 discloses a method of producing polyester by esterifying terephthalic acid, adipic acid and 1,4-butanediol in the presence of titanium compound and a pentavalent phosphorus compound. U.S. Pat. No. 6,303,738 B1 discloses a process for producing copolyester containing adipic acid in the presence of TYZOR IAM (available from DuPont), which was prepared through the combination of TPT (tetraisopropyl titanate) and a mixture of butyl phosphate and dibutyl phosphate. International Patent Application Publication No. WO 2013/033285 relates to an aliphatic-aromatic copolyester of poly(butylene-co-adipate terephthalate) from polyethylene terephthalate, compositions and articles containing the copolyester, a process for preparing the copolyester, and an in situ phosphorus-containing titanium-based catalyst (see abstract, [0001]).
At the end of the polymerization process, the catalyst is typically not quenched (deactivated) in the resin composition. Unfortunately, an active catalyst in the resin composition can sometimes lead to undesirable reactions in subsequent processing of the polyalkylene terephthalate to make blends or compositions. On exposure to high temperature and humidity, blends and compositions containing the modified polyalkylene terephthalate can exhibit hydrolytic degradation, especially under caustic conditions. Another problem associated with some blends is transesterification, which can lead to loss of mechanical properties.
Catalyst quenchers such as phosphoric acid can be added to thermoplastic compositions to prevent such transesterification, but they can also promote degradation of polymer chains and contribute to a decrease in polymer molecular weight and greater hydrolytic instability. The use of phosphite stabilizers is less satisfactory because of the tendency for phosphites to be unstable to both hydrolysis and oxidation. Although the use of chain extenders can help to counterbalance the effect of the quencher, it is desirable to eliminate the use of either quencher or chain extender additives as a necessity.
Insufficient hydrostability of modified polyalkylene terephthalate can lead to chain cleavage, the extent of which depends on the exact conditions of exposure to water or humidity. Temperature, time of exposure, and pH are all important. Both acids and bases can catalyze ester hydrolysis. Decomposition of modified polyalkylene terephthalate can be accelerated in aqueous acid or base, or if the polymer matrix of modified polyalkylene terephthalate contains free acid or base additives. Since a reaction product of polyalkylene terephthalate hydrolysis is itself a carboxylic acid, the hydrolytic decomposition of a polyalkylene terephthalate such as PBT is autocatalytic, as depicted in Scheme 1.

Thus, there is a need for polyalkylene terephthalates with improved properties including hydrostability as well as polymer compositions and articles derived therefrom. There is a further need for new and improved catalysts or processes for the production of modified polyalkylene terephthalates that are effective in polymerization, but that do not adversely impact the properties of the resulting modified polyalkylene terephthalate. There is also a need to eliminate the necessity of using either quencher or chain extender additives in preparing modified polyalkylene terephthalates.